In 1673 Spinoza was invited to Utrecht to meet Louis II, prince de Condé, whose armies had occupied much of the Netherlands since 1672. There he also met the French poet Saint Évremonde. When he returned to The Hague with presents from the prince, he was immediately accused of being in league with the country’s enemy. One year earlier the political leaders of the Netherlands, Johan De Witt and his brother Cornelius, who had been accused of conspiring against the young prince of Orange, William III, had been torn apart by an angry mob. At this point Spinoza, concerned for his safety, seems to have wanted to leave the Netherlands, and he considered an invitation from Louis II to move to Paris, as well as an offer of a professorship from the University of Heidelburg. He ultimately decided against going to Paris, because he feared that Louis did not have enough power to protect him from bigots in France, and he declined the offer from Heidelburg because he did not think he would have complete freedom to teach as he wished. His famous letter to the Heidelburg authorities, which contains an impressive defense of academic freedom, may in fact have been composed after the offer was withdrawn. At any rate, Spinoza seems to have reconciled himself to staying in the Netherlands for the rest of his life.

Spinoza resumed work on his masterpiece, the Ethica (Ethics), finishing a five-part version by 1675. He delayed its publication, however, after being advised that it would cause even greater controversy than the Tractatus. It was finally published, together with the Treatise on the Emendation of the Intellect and an unfinished work on politics, the Tractatus Politicus, at the instigation of some of his Collegiant friends a few months after his death in 1677.

The bulk of the Ethics is written as a geometric proof in the style of Euclid’s Elements, though its more direct inspiration was probably Proclus’s Institutio theologica (Elements of Theology), an axiomatic presentation of Neoplatonicmetaphysics composed in the 5th century ce. Spinoza apparently believed that a geometric presentation of his ideas would be clearer than the conventional narrative style of his earlier works. Accordingly, he begins with a set of definitions of key terms and a series of self-evident “axioms” and proceeds to derive from these a number of “theorems,” or propositions. The early portion of the work contains no introductory or explanatory material to aid the reader, apparently because Spinoza initially thought it unnecessary. By the middle of Part I, however, he had added various notes and observations to ensure that the reader would understand the significance of the conclusions being developed. By the end of Part I he had also added polemical essays and introductions to various topics. The form of the work as a whole is therefore a mixture of axiomatic proof and philosophical narrative.

The Ethics relies on three Jewish sources, which were probably familiar to Spinoza from his early intellectual life. The first is the Dialogues on Love by Leone Ebreo (also known as Judah Abravanel), written in the early 16th century. Spinoza had a copy in Spanish in his library. This text is the source of the key phrases that Spinoza uses at the end of Part V to describe the culmination of human intellectual activity—namely, seeing the world “from the aspect of eternity” and having as an ultimate aim the “intellectual love of God.” Spinoza also used at least one argument from the 15th-century Spanish Jewish philosopher Hasdai ben Abraham Crescas, whose critique of Aristotle had been printed in the mid-16th century in Hebrew. Last, Spinoza seems to have had access to the Gate of Heaven by Abraham Cohen de Herrera, the most philosophically sophisticated Kabbalist of the 17th century. A disciple of Isaac ben Solomon Luria and an early member of the Amsterdam congregation, Herrera knew a vast amount of ancient, Islamic, Jewish, and Christian philosophy, as well as Kabbalistic thought. The Gate of Heaven, his major work, circulated in Amsterdam in Spanish and appeared in a Hebrew abridgement in 1655.

Spinoza begins by stating a set of definitions of eight terms: self-caused, finite of its own kind, substance, attribute, mode, God, freedom, and eternity. These definitions are followed by a series of axioms, one of which supposedly guarantees that the results of Spinoza’s logical demonstrations will be true about reality. Spinoza quickly establishes that substance must be existent, self-caused, and unlimited. From this he proves that there cannot be two substances with the same attribute, since each would limit the other. This leads to the monumental conclusion of Proposition 11: “God, or substance consisting of infinite attributes, each of which expresses eternal and infinite essence, necessarily exists.” From the definition of God as a substance with infinite attributes and other propositions about substance, it follows that “there can be, or be conceived, no other substance but God” (Proposition 14) and that “whatever is, is in God, and nothing can be or be conceived without God” (Proposition 15). This constitutes the core of Spinoza’s pantheism: God is everywhere, and everything that exists is a modification of God. God is known by human beings through only two of his attributes—thought and extension (the quality of having spatial dimensions)—though the number of God’s attributes is infinite. Later in Part I, Spinoza established that everything that occurs necessarily follows from the nature of God and that there can be no contingencies in nature. Part I concludes with an appended polemic about the misreading of the world by religious and superstitious people who think that God can change the course of events and that the course of events sometimes reflects a divine judgment of human behaviour.

Part II explores the two attributes through which human beings understand the world, thought and extension. The latter form of understanding is developed in natural science, the former in logic and psychology. For Spinoza, there is no problem, as there is for Descartes, of explaining the interaction between mind and body. The two are not distinct entities causally interacting with each other but merely different aspects of the same events. Spinoza accepted the mechanistic physics of Descartes as the right way of understanding the world in terms of extension. Individual physical or mental entities are “modes” of substance: physical entities are modes of substance understood in terms of the attribute of extension; mental entities are modes of substance understood in terms of the attribute of thought. Because God is the only substance, all physical and mental entities are modes of God. Whereas the modes are natura naturata (“nature-created”) and transitory, God, or substance, is natura naturans (“nature-creating”) and eternal.

Physical modes that are biological have a feature beyond simple extension, namely, conatus (Latin: “exertion” or “effort”), a desire and drive for self-preservation. Unconsciously, biological modes are also driven by emotions of fear and pleasure to act in certain ways. Human beings, as biological modes, are in a state of bondage as long as they act solely from emotions. In Part V of the Ethics, “Of Human Freedom,” Spinoza explains that freedom is achieved by understanding the power of the emotions over human actions, by rationally accepting things and events over which one has no control, and by increasing one’s knowledge and cultivating one’s intellect. The highest form of knowledge consists of an intellectual intuition of things in their existence as modes and attributes of eternal substance, or God; this is what it means to see the world from the aspect of eternity. This kind of knowledge leads to a deeper understanding of God, who is all things, and ultimately to an intellectual love of God (amor Dei intellectualis), a form of blessedness amounting to a kind of rational-mystical experience.

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